Isolated cleft palate is the commonest craniofacial birth anomaly (e.g., 4.5 per 10,000 births in the US). It creates problems in feeding, speech, hearing, and dental development. Unsuccessful surgery may fail to resolve these problems and reduce the child's potential for social development and inclusion. There is an inadequate evidence base for selecting the optimal timing for surgery, but a possible case for undertaking surgery at 6 months, rather than the more usual timing of 12 months or later. Providing a functioning palate when speech skills begin to develop may lead to better speech outcomes. Our randomized control trial comparing surgery at 6 months or 12 months in infants with isolated non-syndromic cleft palate (funded by NIDCR grants 1U01DE018664 and 1U01DE018837) began recruitment in September 2010. By June 2015, a total of 650 infants will have been recruited across 23 cleft centres in the United Kingdom, Scandinavia and Brazil. From July 2015, over the remaining 5 years of the study, we will follow every child, obtain standardised records at age 12 months, 3 years and 5 years, and compare a variety of outcomes. The main outcome will be the quality of speech (resonance, nasal airflow) as assessed by blinded listeners. Secondary outcomes will include articulation, surgical complications, hearing, growth, and dentofacial development. If significant differences are demonstrated, it is possible that improved knowledge about optimal timing will improve speech quality, and in turn, the social integration of affected children, while reducing the burden of remedial care that they and their families must endure, and the associated medical costs. The findings will be applicable to any country where cleft surgery can be planned in advance.